Any tips to entertain a teenager and 4yo in London this evening?

[Slidyslide]

We're in London for a few days as 15yo dad is attending workshops during the day whilst 4 yo and I sightsee etc.
However older dd has asked if we can do 'something' when she finishes at 4.30 today; younger dd is exhausted so the latest she can stay up is around 8pm... can anyone suggest something that might appeal to both of them (or that the 4yo will at least tolerate?!). Budget isn't huge and I don't want to stray too far from central London.
Any suggestions would be much appreciated!

V and A museum for the fashion (& perhaps pop over the road for the dinosaurs)?

Carnaby St and esp Choccywoccydoodah?

Leicester Sq for people watching and a trip for personalised m and m in m and m world?

Bloomsbury Lanes bowling alley and diner.
If you don't mind a little tube journey, there's a really cool high tech crazy golf course called Puttshack at Westfield at Shepherd's Bush. There's also a bowling alley there. If your older daughter wanted to do some shopping too, you could take your 4yo to Playworld between Debenhams and Next on the Ground Floor.
Visit Magnum Pleasure Store and make your own Magnum desserts in Covent Garden. www.magnumicecream.com/uk/pleasure-store.html

These are great ideas and I wouldn't have thought of any of them, thank you. Will see what she would like to do!

Leicester Square - watching the buskers (often MT students), Lego shop & M & M world.

Covent Garden - shopping for the teen (make up, dancewear, market etc) Buskers & Disney shop for the 4 year old plus there is the Disneytheatre Pop Up with make up, costumes, behind the scenes stuff etc (not sure of opening hours) I think this week is Aladdin based and next week Lion King

We've spent most of the week in Covent Garden- I think dd2 just sighs when we go back now! Leicester Square is sounding like a good plan though, thanks!

Whereabouts is she travelling from?